When an opponent's monster declares an attack: Send 1 "Crystal Beast" card from your Spell & Trap Card Zone to the Graveyard to target the attacking monster; negate the attack, then you can add 1 "Rainbow Dragon" or "Rainbow Dark Dragon" from your Deck to your hand.
Sends 1 “Crystal Beast” from your Spell/Trap zone to your Graveyard, to negate an opponent’s monster attack.
Subsequently searches for Rainbow Dragon from your Deck to your Hand.
Requires “Crystal Beast” monsters in your Spell/Trap zone in order to activate this card.
This card is essential in searching out Rainbow Dragon to your hand as soon as possible.
Since you can still Special Summon Rainbow Dragon with “Crystal Beast” monsters in your Graveyard, it does not matter if you need to send them from your Spell/Trap zone to the Graveyard in order to activate Rainbow Path.
Crystal Blessing is able to quickly retrieve up to 2 “Crystal Beast” monsters from your Graveyard to your Spell/Trap zone. Crystal Beast Sapphire Pegasus is able to place 1 “Crystal Beast” monster from your Deck to the Spell/Trap zone, upon Summoning.
Sends from field to Graveyard / Adds from Deck to hand
They usually avoid releasing cards that mention cards not available in Duel Links.
That being said, I'd imagine the reason we have Path is because it doesn't name any cards in the OCG. It searches for an Ultimate Crystal card, it just hasn't had its TCG text updated. (Which doesn't matter, since those are the only 2 Ultimate Crystals Path can search and nothing cares that it names cards.)